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Naturalists have assumed that streetlights have a negative effect on moths pollinating plants at night. But this is not supported by a carefully constructed study recently published in Ecosphere. The researchers compared the pollination success of a common flower (Silene latifolia) under no lighting, high pressure sodium lighting and LED lighting. They also tested for differences in sites that were lit all night or only for part of the night.
The researchers were expecting to find pollination not as good under lights because the moths would be attracted to the light rather than the flower. But the researchers concluded that “S. latifolia plants in the vicinity of FN [full night] lighting appeared to have enhanced pollination success compared to plants in unlit controls; this result was in direct contrast to the reduction in pollination success and quality under lighting that we had hypothesized.” In other words, pollination of the plant they were studying was better under lights kept on all night than at sites where there was no lighting.
As for LED lighting causing any problems, the team says, “we did not find any difference in pollination success between flowers under HPS lights and those under LEDs”.
The team also found that there was no difference between the sites that had no lighting and those that were only lit for part of the night. The researchers say that this “appears to support our hypothesis that PN [part night] lighting would cause less ecological disruption (relative to unlit controls) than FN [full night] lighting.” So it supports the idea that turning off streetlights when they are not needed from around midnight to dawn has the same effect as the natural state of darkness. Lighting for part of the night doesn’t interfere with nature.
The concern is that “Potentially, lights could act as ecological traps, retaining an artificially high density of moths in their vicinity and leading to locally elevated rates of flower visitation”. So flowers left in the dark might be left without their nocturnal pollinators.
So why are the moths happily pollinating the flowers that are lit all night? The authors of the study speculate that “lighting might increase the visibility of S. latifolia flowers to moths.”
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